besides quality. The OEM pumps have a lip on the snout of the casting that locates the bearing cartridge. Some of the aftermarket pumps do not and rely only on a press fit to hold the cartridge in place. The fan will pull the bearing assembly out the front until the impeller hits the inside of the housing or the belt comes off.
I would not reuse the OEM pump unless it was very low mileage. Do not use GMB pumps since that's the brand I had the bearing come out of. I'm currently running an A1 Cardone pump (new not rebuilt) without problems. This is actually the second A1 pump I've used and the first made it 60k miles without problems. OEM would still be best especially if changing a pump is a big deal for you.